The present disclosure relates to a method and an apparatus for computer-implemented processing of SAR raw data.
SAR systems (SAR=Synthetic Aperture Radar) enable a remote sensing of the earth's surface by detecting radar pulses reflected at the earth's surface, which are emitted by a radar device which moves at a constant speed over the earth's surface in a so-called azimuth direction. The term earth's surface is to be understood broadly and may also relate to the surface of another celestial body (preferably another planet) than the earth.
The SAR raw data detected by an SAR system contain, for a plurality of emitted radar pulses which correlate with corresponding azimuth positions, respective data samples for a plurality of so-called range positions, which represent different distances between the earth's surface and the azimuth direction and, thus, represent radar echoes from different directions. The range positions can also be specified as a so-called slant range (slant distance) or as a so-called ground range (ground distance). The slant range corresponds to the distance of the radar device from the earth's surface in the direction from which a radar echo is received. The ground range corresponds to the projection of the slant range onto the earth's surface. Both quantities can be converted into one another.
In conventional SAR systems, there is the problem that in the SAR raw data an overlap of different radar pulses can occur due to the simultaneous reception of their echoes, resulting in a deterioration in the quality of the processed SAR images. Radar echoes that are received by the radar device from the nadir, i.e. from the direction perpendicular to the earth's surface, are regarded as particularly disturbing.
In order to prevent the simultaneous reception of radar echoes in SAR systems, the pulse repetition rate of the radar pulses and the position and width of the swath of the earth's surface detected by the SAR system can be suitably matched to one another, as a result of which radar echoes from this swath are always received at different points in time. As a result, however, the swath width is limited. It is also known to emit the radar pulses as waveforms which are orthogonal to one another. Although the effect of the overlapping of simultaneously received echoes is thus reduced, there continues to be a clearly perceptible loss of quality in the SAR images.